When a person picks up a telephone and dials a particular number, the dial tones which are input to the telephone are sent to one telephone switch which may make a connection with another telephone switch for directing the call to the desired number. An amount of time must elapse between when the caller inputs the last digit to his telephone and when he receives a ring back from the destination telephone. This elapsed time is known as post-dial delay.
The post-dial delay is a characteristic (parameter) of a telephone network, in that it is different for different telephone connections. In fact, a post-dial delay is a function of the following: the speed with which a user dials his telephone; the type of connection to a long distance switch; the path through which the call is routed from the caller telephone to the receiver's telephone; and the type of PBX the user's telephone or the receiver telephone is connected to, if private branch exchanges are involved.
With reference to FIG. 1, a typical connection between caller telephone 2 and a receiver telephone 4 is shown. As was discussed previously, the digits that a caller inputs to his telephone are sent to a switch 6 and routed across telephone network line 8 to another switch 10, from whence the call is further routed to receiver telephone 4 via line 12. Ordinarily, the post-dial delay comprises the time between the input of the last digit by the caller and the ring back, from telephone 4. Thus, by measuring the post-dial delay, the time needed for a signal to cascade from telephone 2 to telephone 4 can be ascertained. This measurement of the post-dial delay is a characteristic of the telephone network which includes switches 6, 10 and the line leading from telephone 2 to switch 6 and lines 8 and 12.
Oftentimes, however, a user may want to obtain information from an operator or make an operator assisted call. This is done by routing the call to a switch exchange, such as 14, where a number of operators are located. Inasmuch as the number of incoming calls are likely to exceed the number of operators available, the calls are first sent to an auxiliary switch 16 and held in a queue 16a, so that the incoming calls are answered by the operators in a first in first out manner. Thus, when a caller attempts to call an operator, the call is first routed to auxiliary switch 16 and a ring back is provided thereby. After a few rings, an available operator would answer the call and assist the caller. This is all well and good so long as there are sufficient number of operators to handle the incoming calls. However, if there is insufficient number of operators, queue 16a can grow quite lengthy and the caller will be on hold for a long time. When this occurs, most callers would just hang up. Consequently, charges that otherwise would have been earned from operator assisted calls are lost.
Likewise, when a caller is making a credit card call, in most instances the call is routed, after switch 6 and switch 10, to credit card switch 18 via line 20. A signal such as a bong tone is then provided by credit card switch 18 back to telephone 2 to inform the caller to input the desired credit card number. If the correct credit card number is input, usually the call is routed to telephone 4 via line 22. However, if the wrong credit card number was input, usually after several attempts, the call is routed to switch exchange 14 via line 24, so that an operator can intercept the call. If the correct information can then be obtained at that time, the call is routed from switch exchange 14 to line 26 and then telephone 4. Like the queue formed at auxiliary switch 16, if the caller has to wait an inordinate amount of time before an operator answers, chances are the caller will hang up. Accordingly, potential charges are lost.
Thus, there is a need to provide a sufficient number of available operators at switch exchange 14 to handle the incoming calls. But insofar as the demand for operator assisted calls varies throughout the day--for example the demand is much lower at 3:00 a.m. than at 11:00 a.m. or 1:00 p.m.--and the cost of maintaining a large number of idle operators is substantial, the number of available operators must be balanced against the various demand call patterns occurring throughout the day.